1. Field of the Invention
The present invention relates to an image projection apparatus or a projector capable of correcting a trapezoidal distortion of a projected image.
2. Description of the Related Art
An image projection apparatus including an optical image generating unit to generate an optical image and a projection optical system that includes a first optical system including a plurality of lenses and a second optical system formed of a concave mirror, is conventionally known. In this image projection apparatus, the first optical system forms an intermediate optical image, between the first and second optical systems, coupled with the optical image formed in the optical image generating unit, and the second optical system projects the image coupled with the intermediate optical image onto a projection surface such as a screen. When a vertical position of the projected image formed on the projection surface needs to be adjusted, the second optical system is rotated so as to change a posture of the second optical system, whereby the projected image is shifted in a vertical direction and the position of the projected image is adjusted. However, when the posture of the second optical system is changed and the projected image is vertically shifted, a so-called trapezoidal distortion, in which the projected image is distorted in a shape of the trapezoid, occurs to the projected image.
JP-2010-197837-A discloses an image projection apparatus configured to correct the trapezoidal distortion by accommodating a polarization element between the second optical system and the projection surface. The projected image is formed on the projection surface from the second optical system via the polarization element and the corrected image is formed by adjusting the polarization angle of the polarization element.
However, the above technique requires provision of additional optical parts such as the polarization element to correct the trapezoidal distortion and an additional mechanism to drive those optical parts, thereby increasing the number of parts and increasing the cost of manufacturing the apparatus. In addition, there is a problem that the size of the final product increases as the number of parts increases.